1. Field of Invention
The invention relates generally to an image reading device and an electronic whiteboard including the image reading device and, more particularly, to the image reading device and the electronic whiteboard capable of reading data of images written in at least two colors.
2. Description of Related Art
A known electronic whiteboard electrically reads images, such as text/graphics written on a whiteboard or a movable sheet, and records the read images on a recording medium. More specifically, the text/graphics written on the whiteboard or the movable sheet are read by a charge coupled device (CCD). Thereafter, print data for the text/images is created and printed by a thermal printer on the recording medium, such as heat-sensitive paper.
Recently developed is a multi-color electronic whiteboard that reads multi-color images written on a whiteboard or a movable sheet and may perform multi-color printing. Such multi-color electronic whiteboards are disclosed in U.S. Pat. No. 4,789,872 and Japanese Unexamined Patent Publication No. 1-184197.
However, a CCD that employs a fluorescent lamp has some problems, such as the light amount of the fluorescent lamp is unstable, due to the temperature characteristics of the lamp, and the operating life of the lamp is relatively short. In addition, an image reading device included in the electronic whiteboard tends to become large in size, to ensure an optical path to the CCD. Consequently, the size of the electronic whiteboard becomes larger.
The applicant of the invention described later herein has created devices having a multi-color image reading device and a prototype electronic whiteboard that uses a light-emitting diode (LED) and a contact image sensor (CIS), to ensure the stable light amounts for a long time as well as to reduce the size of the image reading device.
The prototype electronic whiteboard includes a whiteboard, a CIS, provided with photo detectors corresponding to the number of pixels, to read images written on the whiteboard, and a red LED and a green LED that emit red light and green light, respectively, to reading positions of the images written on the whiteboard. As shown in FIG. 11, the red LED and the green LED of the prototype electronic whiteboard are, by turns, switched on. The images written in red and black on the prototype electronic whiteboard are stored, as image data in which the colors of the images are identified, based on a first image data A and a second image data B read by the CIS during the emission of the red and green light. Finally, by applying heat, based on the stored image data, to multi-color heat-sensitive paper, which may color in red and black, according amounts of heat applied thereto, the images written on the prototype electronic whiteboard are reproduced on the multi-color heat-sensitive paper.
The CIS, used in the prototype electronic whiteboard, has a charging period of 4.8 msec, as shown in FIG. 11. The CIS is provided with photo detectors corresponding to the number of pixels. Each of the photo detectors requires 4.8 msec to store enough electrical charge, to ensure effective image data, by receiving light. In the CIS, as the photo detector, corresponding to the first pixel, receives the light and stores enough electrical charge to ensure the effective image data, the image data of the first pixel in one line is output by discharging the electrical charge. Typically, the electrical charge is discharged, in turn, from the first photo detector to the last one, for all pixels, after the charging periods thereof After the electrical charge is discharged from the last photo detector, the electrical charge is discharged again from the first photo detector which has stored the electrical charge during the charging period. The charging period is the time during which enough electrical charge is stored to ensure effective image data after a photo detector starts to receive the light. The charging period of the CIS is determined according to the characteristics thereof.
The CIS may discharge the electrical charge even when each of the photo detectors does not store enough electrical charge. It is possible to discharge the stored electrical charge from each of the photo detectors before the charging period elapses. In this case, each of the photo detectors has not yet stored enough electrical charge to ensure effective image data.
However, the image reading device, which is included in the prototype electronic whiteboard, has the following drawbacks. When the CIS having a charging period of 4.8 msec is used, timing pulses TG are output to the CIS at intervals of 4.8 msec, as shown in FIG. 11. The images written on the whiteboard are read by the CIS, while red and green light is, by turns, emitted from the red and green LEDs, respectively. However, the outputs produced by the CIS are affected by both the red and green light, due to the charging periods of the photo detectors corresponding to the number of pixels. Consequently, the images written in red and black on the prototype electronic whiteboard cannot be precisely identified. The problems encountered in the prototype electronic whiteboard led to the invention described below.
Accordingly, one aspect of the invention is to provide a multi-color image reading device employing a contact image sensor (CIS), that precisely identifies multi-color images written on a whiteboard.
Another aspect of the invention is to provide a multi-color image reading device employing a CIS, that precisely identifies multi-color images written on a whiteboard and that reads the images as fast as possible.
According to one aspect of the invention, an image reading device of the invention that reads an image written in at least two colors on a writing surface, by identifying the colors of the image, may include a contact image sensor provided with photo detectors corresponding to a number of pixels, for reading the image written on the writing surface, the contact image sensor having a predetermined charging period; a first light-emitting device that emits a first color of light at an image reading position on the writing surface; a second light-emitting device that emits at an image reading position on the writing surface, a second color of light different from the first color of light; an image data output device that outputs the image written on the writing surface, as image data, by identifying the colors of the image, based on the image data read by the contact image sensor, while the first light-emitting device and the second light-emitting device, are in turn, turned on; and an image reading control device that operates the image data output device, so as to lose a first image data and to adopt a second image data, when each of the photo detectors of the contact image sensor reads the image as the image data by storing an electrical charge while either one of the first light-emitting device and the second light-emitting device emits light corresponding the first color of light or the second color of light.
In the image reading device of the invention, the image reading control device operates the image data output device, so as to lose the first image data and to adopt the second image data, when each of the photo detectors of the contact image sensor reads the image as the image data by storing the electrical charge while either one of the first light-emitting device and the second light-emitting device emits light corresponding to the first color of light or the second color of light. Consequently, the image written in at least two colors on the recording medium may be read while colors of the image are precisely identified.
According to another aspect of the invention, an image reading device of the invention that reads an image written in at least two colors on the recording medium, by identifying the colors of the image, may include a contact image sensor provided with photo detectors corresponding to a number of pixels, for reading the image written on the writing surface, the contact image sensor being divided into a plurality of parts in a direction of a length thereof, the contact image sensor having a predetermined charging period; a first light-emitting device that emits a first color of light, at an image reading position on the writing surface, the first light-emitting device being divided into a plurality of parts in a direction of a length thereof; a second light-emitting device that emits a second color of light at an image reading position on the writing surface, the second light-emitting device being divided into a plurality of parts in a direction of a length thereof; an image data output device that outputs the image written on the writing surface, as image data, by identifying the colors of the image, based on a first image data started to be read by the contact image sensor, during emission of the first color of light from the first light-emitting device, and a second image data started to be read by the contact image sensor, during emission of the second color of light from the second light-emitting device, as the first light-emitting device and the second light-emitting device are by turns, turned on; and an image reading control device that operates the plurality of parts of the contact image sensor, in a predetermined order, and operates the plurality of parts of the contact image sensor so as to lose the image data which is output, while each of the plurality of parts of the contact image sensor performs an effective reading, by other parts of the contact image sensor. The image reading control device executes a reading of the image written on the writing surface by overlapping periods of image reading by each of the plurality of parts of the contact image sensor.
In the image reading device of the invention, the contact image sensor, the first light-emitting device, and the second light-emitting device are divided into parts. The image reading control device operates the plurality of parts of the contact image sensor in a predetermined order. The image reading control device operates the plurality of parts of the contact image sensor, so as to lose the image data which is output while each of the plurality of parts of the contact image sensor performs an effective reading by other parts of the contact image sensor. Further, the image reading control device executes a reading of the image written on the recording medium by overlapping periods of image reading by each of the plurality of parts of the contact image sensor. Consequently, the image written in at least two colors on the writing surface may be read while colors of the image are precisely identified. In addition, the image reading speed is increased.